I just flashed to 0403 bios via in bios Ez flash2 bios update. Now testing away..

new item in 0403 bios:

Added i see is FSB strap to North Bridge which basically lets you set the Strap used between AUTO/200/266/333. Note, what dividers you have available depends on the strap you select if you choose a setting other than AUTO. Basically the same as older bioses just they did the divider choices for you behind the scenes depending on your FSB selected. i.e. set 266FSB with 266 strap and you won't get 1:1 divider which is same as before. I just leave it at AUTO for it to function like past bios for now.

Okay seems 0403 bios has been removed from their server leaving the 0404 bios there.

Asus P5K Deluxe uses 2MB sized bios flash ROMs. So best way to flash or update your bios on Asus P5K Deluxe is to use a USB flash drive and the motherboard's own inbuilt EZ Flash 2 function:

Even at stock cpu/mem speeds, you need to test for stability in memtest86+ v1.70 and windows before attempting to flash your bios. Don't assume stock cpu/mem speeds means stable as AUTO sub timings or some voltages might not be the right stable combination for your component configuration.

Put bios on USB drive

Ensure USB legacy is enabled and boot into bios

Use EZ Flash 2 in bios to select the bios on your usb drive.

Follow prompts to flash and wait until the auto reboot happens.

Sometimes it may not boot up straight away, so turn off system, clear CMOS and you should be up and running again.

Okay can confirm 0404 bios has been tweaked with tighter latencies and more bandwidth that 0311/0403 bios.

With the below settings memtest86+ v1.70 reported bandwidth for the bioses are as follows:

0311 bios = 6015 MB/s

0403 bios = 6012 MB/s

0404 bios = 6250 MB/s <-- unstable for me at below settings errors in memtest which I assume is why bios hangs with the below settings. Tried disabling DDRAM Static read or setting sub timings at AUTO and made no difference. Raising NB volts from 1.55v to 1.70 helped lessent memtest86+ v1.70 test #5 errors but still they existed.

I flashed back to 0311 bios and same settings below are again stable for me. So I guess i'd need to loose subtimings more on 0404 bios to get things stable - I wonder if it will effect max memory clocking frequency though with 0404 bios versus previous bioses ?

Update: with 0311 bios and below settings i changed TRTP: from 8 to 3 and memtest86+ v1.70 reports 6249 MB/s bandwidth now close to that of 0404 bios but it's stable in memtest86+ v1.70 so far. I'd probably stick with 0311 bios for this reason